Optical recording and reproducing device

Abstract

In an optical recording and reproducing device, an aperture member is provided in a region between an objective lens and a reflection mirror so as to be freely pushed into and pulled out of a light flux, and a masking member is provided on the objective lens. The masking member has an inside diameter smaller than an aperture diameter of the aperture member, and has an outside diameter greater than the aperture diameter of the aperture member. The aperture member has an outline size greater than a size of an aperture of an objective lens holding member. Therefore, an effective numerical aperture of the objective lens is determined in accordance with the inside diameter of the masking member in the case where the aperture member is placed in the light flux, whereas the effective numerical aperture is determined by the aperture of the objective lens holding member in the case where the aperture member is not placed in the light flux. With this arrangement, stable reproduction of a compact disk without being affected by a shift of the objective lens is enabled, while reproduction of a high-density disk is also enabled.

What is claimed is: 
     
       1. An optical recording and reproducing device, comprising: a light source for emitting a light beam to be projected on an information recording medium;   an objective lens for converging the light beam on the information recording medium;   an objective lens holding member for holding said objective lens;   a first aperture member for changing a light flux diameter of the light beam, said first aperture member being provided in an optical path of the light beam, between said light source and said objective lens; and   a second aperture member having an aperture diameter smaller than an aperture diameter of said objective lens holding member as well as smaller than an aperture diameter of said first aperture member, said second aperture member being concentric with said objective lens and moving in an interlocked manner with said objective lens.   
     
     
       2. The optical recording and reproducing device as set forth in claim 1, wherein said first aperture member is provided separate and independent of said second aperture member. 
     
     
       3. The optical recording and reproducing device as set forth in claim 1, wherein: said first aperture member is movably provided so as to be freely installable in and removable from the optical path, and blocks light which would pass outside a periphery of said second aperture member in the case where being placed in the optical path; and   said second aperture member has an outside diameter smaller than a light flux diameter in the case where said first aperture is not placed in the optical path, as well as smaller than a diameter of the aperture of said objective lens holding member.   
     
     
       4. The optical recording and reproducing member as set forth in claim 3, wherein: said objective lens is designed so as to be suitable for a first information recording medium; and   said second aperture member has an aperture diameter suitable for a second information recording medium, the second information recording medium differing from the first information recording medium in substrate thickness.   
     
     
       5. The optical recording and reproducing device as set forth in claim 1, wherein: said first aperture member has an outline size such that said first aperture member partly blocks a light flux proceeding to said objective lens; and   the aperture diameter of said first aperture member is substantially coincident with a mean diameter of said second aperture member, the mean diameter being a diameter of a circle whose circumference falls on center of width of said second aperture member, so that the aperture of said first aperture member coincides with the circle when said first aperture member and said second aperture member are concentrically positioned.   
     
     
       6. The optical recording and reproducing device as set forth in claim 1, wherein said second aperture member is made of half-transparent material. 
     
     
       7. The optical recording and reproducing device as set forth in claim 1, wherein said second aperture member is made of opaque material. 
     
     
       8. The optical recording and reproducing device as set forth in claim 1, wherein said second aperture member is a ring-shaped masking member provided directly on a lens surface of said objective lens. 
     
     
       9. The optical recording and reproducing device as set forth in claim 8, wherein the masking member is a dielectric multilayer film. 
     
     
       10. The optical recording and reproducing device as set forth in claim 8, further comprising: a supporting member provided along a circumference of said objective lens, the masking member being positioned using a position of said supporting member as reference position; and   a connecting member for connecting said supporting member and the masking member.   
     
     
       11. The optical recording and reproducing device as set forth in claim 1, wherein said second aperture member is provided close to said objective lens, and includes a transparent plate having a ring-shaped masking member. 
     
     
       12. The optical recording and reproducing device as set forth in claim 1, wherein said second aperture member is a ring-shaped surface portion of one of surfaces of said objective lens, the ring-shaped surface portion being arranged so as to differ in cross-sectional shape from the other surface portion of said objective lens having an ordinary cross-sectional shape for a lens, the ring-shaped surface portion being formed so that light passing therethrough is not converged on the information recording medium. 
     
     
       13. The optical recording and reproducing device as set forth in claim 12, wherein the ring-shaped surface portion has a cross-sectional shape of a concave. 
     
     
       14. The optical recording and reproducing device as set forth in claim 12, wherein the ring-shaped surface portion has an L-shaped cross-sectional shape of a concave. 
     
     
       15. The optical recording and reproducing device as set forth in claim 12, wherein the ring-shaped surface portion has a cross-sectional shape of a convex. 
     
     
       16. The optical recording and reproducing device as set forth in claim 12, wherein the ring-shaped surface portion has a cross-sectional shape of crepe. 
     
     
       17. The optical recording and reproducing device as set forth in claim 12, wherein said objective lens is a hologram lens having concentric concaves and convexes in series as said ring-shaped surface portion.